1. Field of the Invention
The present invention relates to a shock-absorbing bearing for a timepiece, comprising a bearing block, a pierced bearing jewel, a seat for positioning this bearing jewel in this bearing block, an endstone, a seat for positioning this endstone in this bearing block, and a shock-absorbing spring to hold said endstone against said positioning seat, this shock-absorbing spring being connected to said bearing block by four linking arms, parallel to a plane containing the pivot axis of said bearing, and forming, on each side of this plane, a suspension element having two of said linking arms connected to each other by a branch in the form of an arc centered on said pivot axis and having a radius different from that of said endstone, these suspension elements being connected to each other by two diametric arms located on either side of a central support element.
2. Description of the Related Art
Shock-absorbing bearings, designed in particular for the balance staff, have been the subject of a large amount of research work which culminated between the early 1930s and the end of the 1950s. There are approximately 400 patents in this field, including 250 in the aforementioned period. The solutions used at the present time are satisfactory on the whole, which doubtless explains why this subject has seen practically no recent development.
One of the essential elements of this kind of bearing is the shock-absorbing spring. It must be remembered that the dimensions of such a spring are less than 2 mm and are generally in the region of 1.5 mm. These dimensions give rise to design problems as regards both the elastic limits and plastic deformation, particularly during the fixing of the spring, the retention of the spring in case of shock, the mounting of the spring, and the mounting and dismantling of the bearing.
With most shock-absorbing springs, it is found that either the shock-absorbing spring must be positioned before the bearing support is pressed into the bridge or plate, making it necessary to extract the bearing support in order to dismantle the bearing, or, if the extraction of the support is not necessary, the hinge of the shock-absorbing spring fails to remain in place when the spring is disengaged from the support, creating a risk of losing the spring which measures less than 2 mm. It should also be added that the springs having a hinge on one end and fastening means on the other cannot be mounted on the support unless the hinge is placed in the part of the support shaped to receive it. The watchmaker must therefore identify the side of the spring acting as a hinge and the site of the bearing support shaped to receive this hinge, which, because of the dimensions, makes handling even more complicated, with the constant risk of losing the spring.
A shock-absorbing bearing of the aforementioned type to which the invention relates, particularly in respect of the shock-absorbing spring, was previously proposed in U.S. Pat. No. 3,306,028. The principal drawback of this bearing arises from the fact that the central support element of the shock-absorbing spring is connected to the bearing support by four arms, each of which has a length which is reduced by half compared with the total dimension of each of the two suspension elements linking the central support element to the bearing support.
In view of the very small dimensions of such a shock-absorbing spring, the halving of the length of the arms linking this central support element to the bearing support gives rise to a problem with respect to the consequent reduction of the elastic limit, so that this limit can easily be exceeded during the fastening of the arms for linking the shock-absorbing spring to the bearing support.
In case of shock, such a shock-absorbing spring can become disengaged more easily, especially if it has undergone plastic deformation during its fitting.